In cryptography, key agreement schemes define a set of rules for how two parties may each choose a secret, and then compute a shared secret based on such choice. Key agreement schemes are sometimes referred to as key exchange or key establishment schemes.
The most famous form of key agreement is referred to as the Diffie-Hellman (DH) key agreement. Various forms of Diffie-Hellman key agreements exist, including elliptical curve forms, which are commonly used on many websites.
However, quantum computers are emerging as a potential computing platform. Quantum computers use “quantum bits” rather than binary digits utilized in traditional computers. Such quantum computers would theoretically be able to solve certain problems much more quickly than classical computers, including integer factorization, which is the strength behind the Diffie-Hellman key agreement scheme.
In particular, Peter Shor formulated Shor's quantum algorithm in 1994. This algorithm is known to attack the Diffie-Hellman key agreement if a sufficiently powerful quantum computer can be built. Utilizing such algorithm, the risk of a quantum computer discovering the secret for one or both parties in a Diffie Hellman key agreement scheme is nonzero. Therefore, counter measures to Shor's algorithm are needed.